A diesel engine (DE) is one of the most efficient internal combustion engines, as it is reduced in the discharge of carbon dioxide (CO2) per constant output and economical so as to be able to use a low-quality fuel such as heavy oil. There is a tendency that the diesel engines are frequently used to prevent global warning. This is because it is reconsidered that cars and a stationary generator using a diesel engine have high energy efficiency with small amount of discharge of carbon dioxide (CO2).
However, a lot of particulate material (DP) in which unburned hydrocarbons are united with soot is discharged from these diesel engines using heavy oil and light gas oil and is to be the main cause behind the pollution and a social problem. Various industries such as diesel engine makers and car makers undergo researches into and developments in the removal of DP and have made studies and inventions concerning filters having excellent ability of removing DP, DP filters (DPF) so devised that the filter is made to carry an oxidation catalyst to oxidize nitrogen oxide (NO) into nitrogen dioxide (NO2) to burn soot, in order to prevent or retard clogging with soot for a long period of time (for example, Non-Patent Document 1).
Many of these technologies intend to filter exhaust gas by passing it through a thin wall porous ceramics several μm in size. Plate or cylindrical filters obtained by calcining metals or ceramics, filters using a honeycomb ceramic porous molded body of which the meshes are alternately filled up and filters using fine metal wire woven fabrics are known. Also, filters obtained by providing these filters with the ability of oxidizing NO into NO2 to oxidize and burn soot with the intention of preventing or limiting clogging of these filters (for example, Patent Documents 1 and 2).
Non-Patent Document 1: Japan Environmental Management Association for Industry, Environmental Management Vol. 37, p 441-449
Patent Document 1: Publication of Japanese Patent Application Laid-Open No. 1-318715
Patent Document 2: Publication of Japanese Patent Application Laid-Open No. 60-235620